1. Field
The present disclosure relates to a cathode active material, a method of preparing the cathode active material, and an all-solid-state battery including the same.
2. Description of the Related Art
A lithium ion secondary battery has a high charge/discharge capacity, a high operation potential, and excellent charge/discharge cycle characteristics. Thus the demand for their use in portable information terminals, portable electronic devices, and small-sized electric power storage devices, as well as in motor cycles, electric vehicles, and hybrid electric vehicles having a motor as a power source, has increased. The battery uses an electrolyte solution that includes a lithium salt in an organic solvent. However, the non-aqueous electrolyte solution is both flammable and capable of leakage. Therefore, in recent years, developing an all-solid-state lithium battery having a solid electrolyte formed of an inorganic material has become a priority. A solid electrolyte is attractive because it may be less flammable and less susceptible to leakage.
A sulfide or an oxide may be used as a solid electrolyte, and sulfide solid electrolytes provide lithium ion conductivity. When cathode active materials such nickel cobalt aluminum acid (LiNi0.8Co0.15Al0.05O2, also referred to as “NCA”) or lithium cobalt oxide (LiCoO2, also referred to as “LCO”) are used with these solid electrolytes, reactions can occur between the cathode active material and the solid electrolyte at their interface during charge/discharge cycles. An interface resistance is thus produced and lithium ion conductivity deteriorates. Additionally, the charging voltage using these materials is limited to 4.0 V or less. Other cathode active materials for use in an all-solid-state battery include vanadium pentoxide (V2O5) and phosphorus pentoxide (P2O5). However, capacity deterioration may still occur with these materials during repeated charge/discharge processes.
Furthermore, the charging voltage of a lithium ion secondary battery having an electrolyte solution may be 4.2 V or higher, so the energy density of an all-solid-state lithium battery needs to be improved.
A cathode active material having a capacity, charging voltage, and capacity retention that are comparable to an aqueous-based lithium ion secondary battery is desirable. Therefore, there remains a need for a cathode active material that is capable of improving discharge capacity and cycle characteristics for use in an all-solid-state lithium battery that has a solid electrolyte.